Do you have the plate that came with topbox? If yes, well, you can use it but you'll need to drill extra holes into the carrier and it'll never be strong enough. I've done it that way and then later purchased SR3112 kit that comes with stronger plate and all metal hardware that uses subframe to support the topbox. It's great now but the carrier has been drilled already. Well, the holes are hidden but anyway. I should've gone with SR3112 or SRA3112 (alloy plate) from the beginning that doesn't need drilling anything into the carrier.